Stand-Alone Microgrid Inverter Controller Design for Nonlinear, Unbalanced Load with Output Transformer

Abstract

This paper proposes a technique that compensates for unbalance and nonlinearity in microgrid inverters with power transformers operating in stand-alone mode. When a microgrid inverter is operating in stand-alone mode, providing high-quality power is very important. When an unbalanced, nonlinear load is connected, zero sequence current and negative sequence current occur, which leads to an unbalanced output voltage. This paper examines why the zero sequence component occurs differently depending on the structure of a three-phase transformer connected to the inverter output terminal, and it proposes a method for controlling the zero sequence component. It also uses a resonant controller to remove the harmonics that correspond to the negative sequence component and the nonlinear component. The proposed elements were verified by a Powersim (PSIM) simulation.

Unified Control Strategy for Microgrid Solid-State Transformers

“…As discussed in chapter 6, [56] proposes a resonant controller to compensate for the 2 nd harmonic in the d-q reference frame, but it is used in the direct fundamental d-q reference frame. It also proposes two more compensators for the harmonics caused by non-linear loads which are tuned to the 6 th and the 12 th harmonics.…”

“…The proportional resonant (PR) controller has the advantage of compensating in the positive and negative sequence simultaneously - [54]. [56] proposes a multi-resonant controller to compensate for the 2 nd harmonic caused by the unbalanced load condition as well as two more compensators for the harmonics caused by non-linear loads. It is possible, or even probable, that the compensation for non-linear load harmonics obscured the fact that the first compensator produces the inverse 5 th and the direct 7 th harmonics.…”

Decentralized Power Management for Electrical Power Systems in More Electric Aircrafts

“…Fault analysis approaches that provide insights on the system behaviors to unsymmetrical faults have been proposed and the response characteristics for various scenarios have been studied using fault models of various distributed energy sources [25,26]. Considering the increased connection of loads in MEA, the effect of constant power loads to dc systems [27] and unbalanced loads to ac microgrids [28] have been studied.…”